The horned lizard is popularly called a "horned toad", "horny toad", or "horned frog", but it is neither a toad nor a frog. The popular names come from the lizard's rounded body and blunt snout, which give it a decidedly batrachian appearance. Phrynosoma literally means "toad-bodied," and cornutum means "horned". The lizard's horns are extensions of its cranium and contain true bone.

The Texas horned lizard is the largest-bodied and most widely distributed of the approximately 14 species of horned lizards in the western United States and Mexico. The length of an average Texas horned lizard is 69 mm (2.7 in) snout-vent length,[6] however the upper boundary for males is 94 mm (3.7 in) and for females it is 114 mm (4.5 in).[7]

Although its coloration generally serves as camouflage against predation, when threatened by a predator, a horned lizard will puff up and become very fat, which causes its body scales to protrude, making it difficult to swallow. The Texas horned lizard, along with at least three other species of the genusPhrynosoma, also has the ability to squirt an aimed stream of blood from the corners of the eyes and sometimes from its mouth for a distance of up to 5 ft (1.5 m). This not only confuses would-be predators, but also the blood is mixed with a chemical that is foul-tasting to canine predators such as wolves, coyotes, and domestic dogs. This novel behaviour is observed to be very effective in defense.

About 70% of the Texas horned lizard's diet is made up of harvester ants, though they supplement these with termites, beetles, and grasshoppers. In recent years, the Texas horned lizard has declined by about 30% of its range, though there is some indication it may be making a comeback. The decline is usually blamed on overuse of pesticides and the spread of nonnative, but highly aggressive and fiercely territorial, red imported fire ants. Both eradicate harvester ant colonies, destroying the horned lizard's principal source of food. The Texas horned lizard is now a protected species, and it is illegal to take, possess, transport or sell them without a special permit.

Horned lizards are primarily studied by researchers at TCU and the nearby Fort Worth Zoo, with raw data and fieldwork done by state employees. Further research toward the preservation of horned lizards is funded by sale of horned lizard "Keep Texas Wild" license plates.[10]

Despite its fierce appearance, Texas horned lizards are extremely docile creatures. Since they have very few natural predators, they are not at all aggressive, and will never bite. Captured horned lizards will lie completely limp in a human's hand or pocket, playing dead, so they made excellent pets before they were threatened. Today, it is illegal to disturb or keep a horned lizard without a state permit.

The Texas horned lizard is a sunbather, and requires bright sunlight to produce vitamin D. Deprived of sunlight, the animal will be unable to produce vitamin D and will suffer from vitamin deficiency. For this reason horned lizards are most often found along the side of roads or other open, rocky areas, where they can lounge and take in sunlight.

Otherwise, horned lizards are most often found near harvester ant hills. Although they prefer to move very little, horned lizards can move quite fast if they feel there is a predator in the area, and will dart into thick grass and foliage to escape. Horned lizards are also excellent diggers, and can quickly burrow underground to escape threats.

Research aimed at preservation has revealed the Texas horned lizard is extremely genetically diverse, and isolated pockets of genetically distinct subspecies have been found throughout Texas. Though each of these subspecies is physically identical to all other subspecies, it is likely that they are specifically adapted for the region in which they are found. This makes it difficult to know how one subspecies would survive if it were reintroduced into a new area.

The most numerous and widespread subspecies of Texas horned lizard is found in the Panhandle region of Texas. Other distinct subspecies have been identified in East Texas, the Hill Country, and along the coastline. It is not known whether these subspecies can reproduce with one another over the long term, making preservation of all of the subspecies even more crucial to the animals' preservation. It is also unknown whether any of these subspecies will show a particular resistance to the pesticides and fire ants threatening them.

^Munger, James C. (1986). "Rate of Death Due to Predation for two Species of Horned Lizard, Phrynosoma cornutum and Phrynosoma modestum". Copeia (American Society of Ichthyologists and Herpetologists) 3 (3): 820–824. JSTOR1444970.